<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      function bank() {
        let surplus;

        let yue = +prompt('输入银行卡余额');
        let Accommodation = +prompt('输入食宿消费');
        let live = +prompt('输入生活消费');

        return (surplus = yue - Accommodation - live);
      }

      console.log(bank());
    </script>
  </body>
</html>
